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Individual complex Dirac eigenvalue distributions from random matrix theory and lattice QCD at nonzero chemical potential
We analyze how individual eigenvalues of the QCD Dirac operator at nonzero chemical potential are distributed in the complex plane. Exact and approximate analytical results for such distributions are derived from non-Hermitian random matrix theory. When comparing these to lattice QCD spectra close to the origin, excellent agreement is found for zero and nonzero topology at several values of the chemical potential. Our analytical results are also applicable to other physical systems in the same symmetry class
Distributions of individual Dirac eigenvalues for QCD at non-zero chemical potential: RMT predictions and lattice results
For QCD at non-zero chemical potential , the Dirac eigenvalues are scattered in the complex plane. We define a notion of ordering for individual eigenvalues in this case and derive the distributions of individual eigenvalues from random matrix theory (RMT). We distinguish two cases depending on the parameter , where is the volume and is the familiar low-energy constant of chiral perturbation theory. For small , we use a Fredholm determinant expansion and observe that already the first few terms give an excellent approximation. For large , all spectral correlations are rotationally invariant, and exact results can be derived. We compare the RMT predictions to lattice data and in both cases find excellent agreement in the topological sectors
A Non-Perturbative Treatment of the Pion in the Linear Sigma-Model
Using a non-perturbative method based on the selfconsistent Quasi-particle
Random-Phase Approximation (QRPA) we describe the properties of the pion in the
linear -model. It is found that the pion is massless in the chiral
limit, both at zero- and finite temperature, in accordance with Goldstone's
theorem.Comment: To appear in Nucl.Phys. A, 16 pages, 2 Postscript figure
Effective Operators for Double-Beta Decay
We use a solvable model to examine double-beta decay, focusing on the
neutrinoless mode. After examining the ways in which the neutrino propagator
affects the corresponding matrix element, we address the problem of finite
model-space size in shell-model calculations by projecting our exact wave
functions onto a smaller subspace. We then test both traditional and more
recent prescriptions for constructing effective operators in small model
spaces, concluding that the usual treatment of double-beta-decay operators in
realistic calculations is unable to fully account for the neglected parts of
the model space. We also test the quality of the Quasiparticle Random Phase
Approximation and examine a recent proposal within that framework to use
two-neutrino decay to fix parameters in the Hamiltonian. The procedure
eliminates the dependence of neutrinoless decay on some unfixed parameters and
reduces the dependence on model-space size, though it doesn't eliminate the
latter completely.Comment: 10 pages, 8 figure
Popularising history: some reflections and experiences.
Paper presented at the Wits History Workshop: The Making of Class, 9-14 February, 1987
Australian telephone network subscription and calling demands: evidence from a stated-preference experiment
This paper examines the impact of the subscription-calling rate structure on the demand for residential telephone network subscription and calling. Stated-preference experimental data are used to estimate demand equations. The results indicate that household network subscription and calling demands for the Sydney Metropolitan Area are affected by both rate structure and household socio-demographic variables.Telecommunications demand; Subscription-calling rate structure; Stated-preference experimental analysis; Survey
Characteristics of Bose-Einstein condensation in an optical lattice
We discuss several possible experimental signatures of the Bose-Einstein
condensation (BEC) transition for an ultracold Bose gas in an inhomogeneous
optical lattice. Based on the commonly used time-of-flight imaging technique,
we show that the momentum-space density profile in the first Brillouin zone,
supplemented by the visibility of interference patterns, provides valuable
information about the system. In particular, by crossing the BEC transition
temperature, the appearance of a clear bimodal structure sets a qualitative and
universal signature of this phase transition. Furthermore, the momentum
distribution can also be applied to extract the condensate fraction, which may
serve as a promising thermometer in such a system.Comment: 12 pages, 13 figures; Revised version with new figures; Phys. Rev. A
77, 043626 (2008
Economies of scale and scope in Australian telecommunications
This paper employs a composite cost function to examine the cost structure of Australian telephone services. The composite cost model combines the log-quadratic input price structure of the translog model with a quadratic structure for multiple outputs. Quadratic output structures permit the measurement of economies of scale, economies of scope, and subadditivity without prejudging their presence. Model estimates, on Telstra system data from 1926 to 1991, show that the production of Australian telephone services exhibits economies of scope but no ray economies of scale.Telecommunications; production; scale; scope; Australia
Labour and capital saving technical change in telecommunications
The Australian telecommunications sector is being improved and extended through substantial recent investment in intelligent technology such as digital switching, fibre optics, satellite and cellular transmission, and the Internet. These technologies are being progressively integrated with technology from the broadcasting, computer and electronics industries, providing a unified information infrastructure for information transmission and processing. Technological progress embodied in new equipment has the effect of increasing the efficiency of the factors of production. Such efficiency increases can be biased towards a particular factor. For instance, the impact of labour-augmenting technical change is a decline in the cost of labour per unit of production. When such biases are apparent the relativity between the costs of labour and capital per unit of production is changed. In the longer term, technical change can impact on the rate of employment growth and also on the rate of capital accumulation. In this study the Australian telecommunications cost structure is examined for the period 1919 to 1988. To measure labour saving and capital saving technical change a translog cost model is estimated. Multiproduct telecommunications cost studies typically employ the translog cost model (Evans and Heckman, 1984; Roller, 1990a; 1990b; Shin and Ying, 1992; McKenzie and Small, 1997). The translog model places no a priori restrictions on substitution possibilities among the factors of production, and allows scale economies to vary with the level of output.
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